بررسی و تحلیل شواهد ژئومورفیک زمین‌ساخت فعال در حوضه رودبار از سرشاخه‌های دز

An Investigation and Analysis of the Active Tectonic Geomorphologic Signs, In the Upstreams of Dez at the Rudbar Basin

Sharifi Najafabadi R.
Ph.D. Candidate of Geomorphology, University of Isfahan
Moairy M.
Assistant Prof. In Geomorphology, University of Isfahan
Ghayoor H.A.
Professor in Geography, University of Isfahan
Shafaei H.
Assistant Prof. in Structural Geology, University of Isfahan
Seif A.
Assistant Prof. in Geomorphology, University Isfahan

Received:03/02/2010 Accepted: 22/04/2010


Extended Abstract

Introduction
Active faults are the ones that at the post - Quaterner and especially the Holocen epoch have had movements and it expects that in the future they also exposure to a relative movement because of their renewed activity and generate a shear on any structures locality on them . To identify these faults, seismogram and historical record information, direct and indirect paleosismology studies are utilized. The indirect paleosismology has been based on geomorphologyic studies. Its advantage is that it studies a wide scope with a high speed and the attained to interpret the changes of thousands years ago. Geomorphologyic indices used to study drainage system condition are influenced by the earth material and region climate as well as tectonic .
Since Iran is the sixth country of the earthquake hazard and the earthquake belt has surrounded 90 % lands of this country, location of the cities and development facilities and installations need to be considered precisely to minimize the dangers. In this regard, identifying the regions and active faults are very important. Rudbar river basin, a upstreams of Dez, located in the middle domain of zagros mountain on eastern 49 ? 12? 31? to 50 ? 17? 45? longitude and northern 32 ? 34? 56? to 33 ? 19? 40? latitude and its area is 2256 km2 in the upstream of Rudbar dam . Wide central and north eastern areas have thrust structures while in south western the folded and faulted structures are in close relationship with each other . However, special professional studies are needed in relation to the spam seismologic . It was identified in an estimation that there are more earthquakes in south western areas .

Materials and Methods
In this paper , Rudbar basin has been divided to seven sub - basins with average length more than 20 kms and using the Relative tectonic activity (lat) index that is a combination of hypsometric integral(Hi),drainage basin shape (BS) , drainage basin asymmetry (AF), ratio of valley – floor width to valley height(Vf) , stream length - gradient indices (SL) . Rudbar basin situation was analyzed to minimize the effects of litology and climate factors. Thus, a digital elevation model related to SRTM topographic data at the accuracy of 90 meter was provided. Then , subbasin divisions , indices measurements , geology maps digitation, and data integration were conducted by using ARCMAP,ARC INFO , and GLOBALMAPER Softwares. To increase the work accuracy and to provide necessary evidence, field studies also were formed .

Results and Discussion
According to Relative Tectonic Activity (lat) index, three class active(lat = 1.5 - 1.99), 1256 km2, semi - active (lat = 2 - 2.49), 414km2 and low - active (lat = 2.5 - 3), 585 km2 were identified. Since a main part of Anooj and Gholyans subbasin has alluvium sediments and old terrace, it may be considered more active than the resulted condition.

Conclusion
The obtained general result shows that instability presents in this district has been the resuit of two types of fault performances: the thrust faults located in the west and east of basin such as Dehsur, Vahdat Abad and Zardkuh which had a progress and caused the elevation of district and Main Recent Fault with strike-slip that caused a crushed surface and sensitive to erosion by its right-side movement and the drop of its level surface and then caused the renewed erosion cycle. Since the desired location for constructing Rudbar dam is located in very active region and in Main Recent Fault direction and different as well as severe earthquakes have taken place on two sides of this domain, there is the possibility of tectonic instability in the domain of this dam. Hence, it is suggested that this issue needs to be considered carefully and seriously by the administrators of this project.


Keywords: Active tectonic , Rudbar basin, Geomorphic indices ,Main recent fault.